The metabolism of permethrin in pyrethroid resistant (ICI-R) and susceptible (LSU-S) tobacco budworm Heliothis virescens (F.), larvae was evaluated by topically treating third and last instar larvae with C(14) radiolabeled permethrin. At 18 hr posttreatment, the resistant larvae treated with permethrin had less total radiolabeled material internal, and less parent than did the susceptible larvae. The metabolism of C(14) amitraz was also investigated in last instar larvae of these two tobacco budworm strains. In contrast to permethrin, no major differences were found at both 4 hr and 18 hr posttreatment in the degree of amitraz metabolism in these two strains of the tobacco budworm. N'-(2,4-dimethylphenyl)-N-methylformamidine (Nor-Am 49844, BTS-27271) was detected as a metabolite of amitraz in both strains of the tobacco budworm. The effect of chlordimeform (CDF), amitraz and 49844 on JH III and permethrin uptake from a treated surface by third instar larvae of the tobacco budworm was determined. Using the uptake of H(3)-JH III by the LSU-S strain as a relative measure of larval movement, both CDF and 49844 were effective in increasing the movement of the larvae, but amitraz was not. When the uptake of permethrin was investigated, only CDF was found to result in a significant increase in permethrin uptake by both strains of the tobacco budworm. The above studies suggest that while the pyrethroid resistant tobacco budworm larvae differ in their ability to metabolize permethrin, this difference in metabolic capability does not appear to extend to amitraz. Compared to amitraz and it's metabolite, 49844, CDF was more consistent in enhancing larval movement and permethrin uptake.